The present invention relates to a method of and an arrangement for monitoring maximum pressing forces in a pelletizing machine which has a rotatable matrix disc and plungers whose maximum pressing forces are supplied for further evaluation to a computer, the computer controls a setting out deflector for defective pellets.
For insuring a predetermined quality of pellets during their manufacture, pressing forces are continuously monitored during the manufacture and compared with nominal values. If a measured maximum pressing force is outside of the nominal value limit, a corresponding pellet is sorted out. This is performed by actuation of a sorting out device located behind a pressing station and particularly behind the main pressing station associated with a prepressing station. The maximum pressing forces of at least the pressing rollers of the main pressing station are measured and evaluated. In view of the high circumferential speed of the matrix disc, the evaluation of the measuring results is performed by a computer, to which the measured pressing force values are supplied. Moreover, it is necessary to supply these signals in the computer, which correspond to the respective position of associated matrix opening or the corresponding plunger during circulation of the matrix disc, for associating an error in the manufacture of the pellets with a corresponding plunger pair, in order to further evaluate the measuring results.
A monitoring of the pressing forces during the manufacture of the pellets is not only required for detecting an error and sorting out of defective pellets but also for monitoring the quality of the produced tablets and to obtain at a later time the information whether the produced tablets correspond to the required quality by determination that the manufacture is performed with a predetermined pressing force. The computer can provided for a continuous control and indication of the measuring results as well as the value of occurring errors.
In order to associate measured maximum pressing forces with the plungers at which they occur, it is known to arrange a plunger proximate switch as a measuring transmitter on the matrix disc, as disclosed in the German document DE-A 2,824,547. It shows the time of each individual pressing force value, at which the maximum pressing force is reached. This is a proximity switch which releases a switching pulse when for example a metal part passes in front of an electrical field. With a matrix disc having for example 30 matrix openings, 30 pulses are therefore released per single revolution and supplied to the computer. A second plunger proximity switch formed as a measuring transmitter is associated in the known pelletizing machine with the above mentioned plunger proximity switch. The pulse length of the second proximity switch is independent from the circumferential speed or the number of revolutions of matrix disc so that an exact determination of the position of the plunger during rotation of the matrix disc at each time point is possible through the computer.
The utilization of the known plunger proximity switch is however not satisfactory when in a pelletizing machine a matrix disc with a predetermined plunger pitch such for example with 30 plungers must be exchanged with another plunger pitch, such as for example 24 matrix openings, or another matrix disc with the same plunger pitch but another property of the matrix openings must be installed for producing bigger or smaller pellets. In the case of such exchangeability of the matrix disc of a pelletizing machine, it is required usually that different products on the same machine can be produced with simple conversion. Since during the production of bigger tablets other matrix openings and correspondingly other plungers are needed then in the case of producing smaller pellets, a smaller number of matrix openings distributed over the periphery of the matrix disc and thereby another number of the plungers is needed. The computation can be performed with the use of predetermined plunger proximity switch with considerable expenses since with a change in the plunger pitch a complete conversion of the approximate switch is required and cannot be performed by operational personnel.